ALADFAR (Eta Lyrae). Lyra, the Lyre or
Harp, is so dominated by the set of six stars that make the
exquisite figure that we barely pay attention to any of the others
in the constellation. Oddly, while only three of the inner six (Vega, Sheliak, and
Sulafat, respectively Alpha, Beta, and Gamma) have proper names, so
does one of the outliers, fourth magnitude (4.39) Eta Lyrae, which
is erroneously called Aladfar (the "talons" of an eagle), the name
apparently stolen from another outlier, Mu Lyrae (Al Athfar).
Aladfar is a hot, blue-white class B (B2.5) subgiant that has
either quit core hydrogen fusion or will do so shortly and that is
beginning its rapid (at least on an astronomical time scale)
evolution toward becoming a red
giant. The temperature is uncertain, having been first
measured at 17,950 Kelvin and later presumably better-determined at
16,045. The latter, however, is more like that of a class B4 star,
whereas the hotter value is more appropriate, and will be adopted
here. Allowance for the star's ultraviolet light yields a
luminosity 6500 times that of the Sun, a
radius of 8.4 solar, and a mass of 7.5 solar or 8 solar depending
on the exact state of evolution, the age around 30 million years.
Unlike many class B stars, Aladfar rotates slowly, the equatorial
velocity greater than or equal to just 10 kilometers per second,
giving a rotation period of 42 days or under. Slow class A or B
rotators frequently have weird chemical compositions that are the
result of diffusion of elements in quiet stellar atmospheres. That
Aladfar is not chemically odd suggests that the rotation velocity
is really much higher and that the star's rotation axis is more or
less pointing at us. About half a minute of arc away lies a class
A0 "companion" that is merely a line of sight coincidence.
Aladfar's spectrum, however,
reveals the possibility of a real close-in companion that orbits
with a period of 56.4 days, but about which nothing is known. If
the companion is like the Sun, it is some 0.6 Astronomical Units
from Aladfar proper. Aladfar appears to be just under the limit at
which stars explode as supernovae, and after
ejecting most of itself back into space through powerful winds will
most likely end its regular life as a massive white dwarf not far from the
1.4 solar mass limit allowed for such stars. However, it might
still provide a spectacular event. If the star's evolution
encroaches on the companion, it might bring the little one close
enough to dump mass on the developing white dwarf so as to overflow
the 1.4 limit, the result again a spectacular supernova.